Barrel Finishing

It's been a while since I've last posted here, so I wanted to take a little time to discuss some of what I've been working on recently.  Barrel finishing isn't a huge job, or too complex, but something worth talking about.  The barrel on the burl-stocked fowling piece project  will be the focus of this discussion. 

This barrel can basically be described as a three stage, octagon to round barrel.  The forward most section is round, the middle section is also round, but separated by wedding bands and the breech section is octagon with decorative file work.  This is a barrel form typically seen on 17th century smoothbore guns. 

Starting barrel profile

Modern barrels with round sections are produced by turning on a lathe.  Done properly, this process efficiently produces relatively true round profiles, but also results in a finish with slight waves and imperfections.  In order to smooth these out, the barrel must be filed or "struck".  Striking a barrel generally refers to using a file length-wise over the barrel surface to create a more consistent surface.  This process is especially important for barrels with "swamp" or curved profiles since these shapes are typically comprised of several straight sections blended together. 

I have found a Vixen file to be useful for this process.  A friend has also suggested a 6-8" section of low angle lathe file to work very well.  In practice the file is held against the barrel in a lengthwise fashion and pushed across this surface.  This process is repeated around the barrel perimeter in order to accommodate the round cross section.  The file will contact the high areas and cut them down to create a relatively smooth contour. 

Striking barrel with Vixen file

After striking the barrel, I use a mill file and draw file the surface.  This improves the finish.  Draw filing is basically a process where a mill file is held more or less perpendicular to the barrel axis.  It can be pushed or pulled and results in shavings produced from a shearing cut.  Finishes from this technique are typically pretty good. ​

Draw filing barrel

The next step is to further smooth the surface using abrasive paper wrapped around a flexible backer material.  I find finishing to 320 grit sufficient for a surface left bright.

Sanding barrel

Finally, working the surface with Scotch-Brite abrasive pads evens things out a bit and improves the finish.

A few notes about striking a barrel...   A round barrel left bright will show even the tiniest waves or imperfection from the turning process, so striking is very important.  On barrels with significant profile, a thinner file can be used so it will bend to shape.  Striking is also useful for octagon barrels where straight segments don't blend well.

As can be seen, the breech section of the barrel shown has a section where the corners of the octagon are removed, creating the appearance of a 16 sided region.  Again, this is typically seen on 17th century work.

A front sight was added to this barrel by cutting a recess and slightly swaging material around the sight, locking it in place.  In practice the sight is slightly upset on the bottom surface allowing for a good mechanical joint.  This fowling piece barrel is relatively thin, but this process can still be used with care.  In this case the sight is iron and the form was taken from a 17th century design by Andrew Dolep.

Front sight

As an aside, here's a final shot showing the sideplate for the burl-stocked gun.  It's interesting that the serpentine sideplate first showed up in Paris around 1670 or so, but continued to see use on trade guns until the second half of the 19th century!  By the very early 18th century, it had become out of fashion on most other work.

Serpentine side plate

Well, that's all for now.  Lots of work to get done as always.  Questions and comments are always welcomed.

Jim